1. Field of the Invention
The present invention relates to an apparatus and method of enhancing the leaching rate of a given material, and is particularly relevant to enhancing the leaching rate of ceramic materials used as cores in the production of cast components.
2. Related Art Statement
Ceramic cores and/or tubes are used to produce intricate cooling paths in, for example, turbine blades. After the casting operation has taken place, the cores are removed by dissolving them in a leaching solution.
At present, there aere basically two types of core material, namely: those having a fully dense structure and those having a structure of interconnecting pores.
During the leaching process, core material is gradually dissolved at the core/solution interface and the reaction product is transported away from the interface by diffusion into the leaching solution. This leads to a concentration gradient of the reaction product within the leaching solution, the concentration being highest near the interface.
Under the conditions outlined above, the leaching rate of a core is determined entirely by the rate of diffusion of the reaction product from the interface to the bulk of the leaching solution.
If, however, the leaching solution is agitated the removal rate of the reaction product can be increased, thus making the leaching rate less dependent on the diffusion of the reaction product through the solution. However, in the case of thin cores or small diameter tubes, after the removal of the first few millimeters of the material, any agitation in the bulk of the leaching solution would have little or no effect on the reaction product at the core/solution interface. This means that the leaching rate would again be dependent on the rate at which the reaction product can diffuse into the bulk of the leaching solution, which is situated some distance away from the core/solution interface. The rate of leaching will gradually decrease with time as the depth of the cavity left by the removal of the core increases.